Reducing liquid level in well tubing



June 28, 1960 w. M. HAGGARD 2,942,663

REDUCING LIQUID LEVEL IN WELL TUBING Filed July 28, 1958 A I? 1* 01K. 7/

20 e A E INVENTOR.

WARD M. HAGGARD ATTORNEY United States Patent REDUCING LI un) LEVEL INWELL TUBING Ward M. Haggard, Sun Oil Co., P.O. Box 2831, Beaumont, Tex.

Filed July 28, 1958, Ser. No. 751,489

2 Claims. (Cl. 166-45) duction, the hydrostatic head of the wash waterin the well tubing often is too great to permit the well to flow. Itthen becomes necessary to reduce the water level in the tubingsutficiently to allow the well to be brought in. Also, during theproducing life of a well, salt water may accumulate in the well tubinguntil the hydrostatic head exceeds the formation pressure, thus stoppingproduction. Likewise in such cases, it is necessary to lower the waterlevel in the tubing so that flow can again be obtained from theformation.

Various methods are known for reducing the water level in well tubing.One procedure involves providing the tubing at a suitable depth in thewell with an unloading valve which can be caused to open by theapplication of air or other gas pressure at the top of the tubing andthus to allow the water to flow from the tubing into the casing annulusand thence out of the casing at the well head. A procedure of this typewhich utilizes an unloading valve positioned on the side of the tubingstring is described in Hodges application Serial Number 659,873, filedMay 17, 1957. Other such procedures employing unloading valvespositioned either as a part of the tubing string or in a side pocketmandrel in the tubing string are described in Hodges applications SerialNumbers 746,276 and 746,277, each filed July 2, 1958. These procedurespermit water to be removed from well tubing after a packer has been setbetween the tubing and casing beneath the level at which the unloadingvalve is located. It is also known to lower the water level in a wellbefore a packer has been set byforcing the water from the bottom of thetubing and thence up the casing annulus.

The usual manner of reducing the liquid level in the tubing, either whenit is provided with an unloading valve above a packer or before settinga packer and without an unloading valve, involves merely forcing a gasunder sufficient pressure into the top of the tubing until the liquidlevel has been lowered to the desired depth. However, this generallyrequires the application of a high pressure due to a progressiveincrease in the gas pressure necessary at the well head during theunloading operation. The procedure is thus both time consuming andexpensive.

The present invention provides an improved method for reducing theliquid level in a well tubing which has a passageway for fluid to flowtherefrom into the casing annulus, such passageway being provided eitherby an unloading valve or the open bottom end of the tubing. Theprocedure not only permits the unloading to be done ice in considerablyless time than heretofore has been possible, but it also permits the useof substantially lower pressures at the well head. This results in amarked reduction in compressor capacity requirements and a correspondingreduction in the costs for carrying'out the operation.

According to the invention the liquid level in a well tubing, which hasbeen provided with an unloading valve located at a depth above thepacker but below the maximum depth to which the liquid level is to bedisplaced or which has no packer and no unloading valve, is firstdisplaced downwardly by forcing a gas into the top of the well tubing.Introduction of the gas is stopped after the liquid level has beenlowered only part way to the desired depth. Then liquid is forced intothe tubing above the gas column until the level of the liquid below thegas has been reduced to the desired depth. This causes progressivecompression of the gas column in the tubing without requiring acorresponding progressive increase in pressure at the well head. At thesame time the bulk of the introduced liquid remains, as has now beendiscovered, as a liquid column above the gas column. After the desiredlowering of liquid level has been secured, pressure is released at thetop of the tubing. This permits expansion of the gas column whichresults in lifting of the liquid thereabove from the well.

The invention is more specifically described with referenoe to theaccompanying drawing which schematically depicts a well provided with apacker and with valve means for unloading liquid from the well tubinginto the casing above the packer.

With reference to the drawing, a well is shown having a casing 10provided with perforations 11 adjacent a production zone designated aszone A. vWell tubing 12 extends inside the casing and a conventionalpacker 13 is positioned for sealing the lower part of the casingannulus. Above the packer the tubing string contains a side pocketmandrel 14 adapted to hold an unloading device 15 located adjacent aport 16 in the mandrel wall. The unloading device 15 can be any known orsuitable tool of this type containing valve means adapted to open whensufiicient pressure is applied in the tubing and thereby permit flow offluid through the device and port 16 into the casing annulus. The tubingstring may, if desired, be provided with a check valve, indicatedschematically at 17, to prevent liquid from being forced back into zoneA whenever pressure is applied to the well tubing.

At the well head a compressor 18 is provided for supplying a gas, suchas air or natural gas, under pressure to tubing 12 via valve 19 and line20. Also a pump 21 is provided for supplying liquid, such as water orcrude oil, to the tubing through line 22 and valve 23. Additionalequipment at the well head includes a pressure gauge 24, a pressurerelease line 25 having valve 26, and a line '27 containing valve 28 forflow of liquid from the casing.

Whenever it is desired to reduce the liquid level in the tubing 12,compressor 18 is started and air or other gas is forced into the tubing.The increase in pressure therein causes the valve in unloading device 15to open and admit liquid to the casing annulus, with liquid beingwithdrawn therefrom through line 27 and valve 28. Preferably the amountof gas forced into the tubing at this stage is at least sufiicient todisplace the liquid level downwardly at distance which is at leastone-half the total desired length of displacement. Introduction of thegas is stopped, however, substantially before the liquid level has beenlowered to the desired depth. After stopping of compressor 18, pump 21is then started and water or other liquid is forced into the tubingabove the gas column. If desired, a separation device may be insortedinto the tubing to precede the liquid from pump 21 so as to prevent anymixing of the introduced liquid attained. This required a time of 8 /3hours.

with the gas. This would be" desirable, for example, it air were used asthe gas while crude oil is used as the hquid; or also if for some reasonthe pressure is not to be released from the tubing until after aconsiderable lapse of time afterxthe desired displacement level has beenreached. However, when employing air and water as'the 7 displacementfluids, no separation device is normally'required forsuccessf uloperation ofthe present method since most of the water' pumped 'inremains above'the air column. 1

After the desired reduction of liquid level has been 'eifected in theabove described manner, the pressure on the well tubing is'released byopening valve 26 in line 25. This allows the gas column, which hadpreviously been progressively compressed as the liquid was pumpedinabove it; to expand and force the liquid ahead of .it out of thetubing through line 25. Thereafter the well can be brought intoproduction from zone A. The foregoing procedure can be employed inessentially the ,same manner for lowering the waterlevel in well tubingbefore a packer has been set. i In such case the unloading device 15,check valve 17 and packer 13 would not be present. Gas followed byliquid would be forced into the tubing in the manner described above,thus causing the water'to flow from the bottom of the tubing "and up thecasing annulus until the desired amount of water 'hadbeen displaced.Pressure would then be released at the well head to permit the gascolumn to expand and force out the liquid above it. Thereafter a packercould be set and the well then brought in on production. a

The following specifically illustrates advantages of the invention: V

A well having a 2" tubing required unloading of the V tubing liquid to a:depth of 7800' in order to maintain flow. When this was done inconventional manner'by '3 pumping in'only airusing a compressor rated at65 cubic feet per minute, the pressure at the top of the tubing had tobe progressively increased to V avalue exceeding 3000 psig before thedesired lowering ofliquid level was Later, the well was'u'nloaded to thesame depth in accordance with the present invention. This was done byfirst forcing in enough air with the same compressor to reduce theliquid level to 3900'. The pressure at the surface dur- 7 ing this stagebuilt up to a maximum of 1500 p.s.i.g. Water was then pumped into thetubing in amount of approxi- 7 required for this operation was 2 /3hours as compared to the 8 /3 hours needed when the conventionalprocedure wasused. 7

I claim: r 1 a 1. Method of removing liquid from well tubing in a casedwell where the hydrostatic head of the liquid column is Vsuchthatthewell will'not flow at the desired rate, said well tubing havinga-passageway through which liquid can be forced from the tubing into thecasing an- "nulus, which comprises introducing a. gas into the top ofthe tubing to effect liquid flow through said passageway, stopping suchintroduction of gas when the level of the liquid in the tubing has beenlowered only part wayto the desired depth, then introducing a liquidintothe top of the tubing to lower the level of the liquid beneath thegas further while compressing thecoli mn of gas thereabove in thetubing, and thereafter releasing pressure at the top of. the well tubingwhereby said column of gas expands and forces the liquidv column 'aboyeit out ofthetubing, V V

2, Method vaccording to claim l wherein the amounts "of gas and liquidintroduced into the well tubing are such that the length of displacementof saidliquid level during introduction of the. gas is at least asmuch'as the length of displacement during introduction of the liquid.

References Cited in the file of this patent 2,808,887 Erwin Oct. 8; 1957

